Dear Autodesk Simulation CFD experts,
I would like to model a thin plate with a bank of holes. The thickness of the plate is 2 mm. The diamter of the holes is 1.5 mm. The distance between each 2 hole center is 4.8 mm. It looks like I can use the K-Factor method. But, how can I find out the K value? Or is there any other method in CFD 2014 that will be more suited for this?
Solved! Go to Solution.
To start you might look at the geometry and compute the Free Area Ratio
You could use this as input to the resistance model.
If you want to compute to a K the equation that would be used is
K = ( [0.707(1-FAR)^0.375 + 1 - FAR]^2 ) / FAR^2
Thanks again for the reply!
So, for a 5X5 holes:
Total area = 24mm X 24 mm = 576 mm^2
Free Area = pi x (1.5 mm)^2 x 25 /4 = 44.18 mm^2
==> FAR = 44.18/576 = 0.0767
However, based on the wikihelp docuement,
The relationship between loss coefficient, K, and free area ratio, FAR, is given as:
You are right, the formula Apolo mentioned is for very thin sheets (t/d<0.015). Yours is a thick sheet and hence the formula will be different,
You can get the constant k-factor by two methods:
1) Use Idelchik's handbook of hydraulic resistance to find the k-factor for your perforated sheet
2) Create a small unitary cell that is symmetrical, and simulate it for velocities, close to your operating velocities, and then calculate the value of k as : k=DP/ (0.5*rho*v^2)
where DP is pressure drop, rho is density of fluid and v is velocity.